1. Technical Field
The invention relates generally to monitoring fluid flow, and more particularly, to detecting upstream fluid occlusions in an intravenous fluid administration system.
2. Background of the Invention
Fluid delivery systems for infusing parenteral fluids are commonly used in hospitals and typically include an inverted bottle or bag or other means of supply of parenteral fluid, an intravenous (IV) administration set and an infusion pump for controlled delivery to a vascular system of a patient. The fluid administration set typically includes a flexible infusion tube, a drip chamber, injection sites among other components, and a catheter mounted to the distal end of the flexible infusion tube adapted to be inserted into the patient""s blood vessel. Commonly, the pump is of a peristaltic type in which a plurality of fingers, rollers, or other devices sequentially constrict the tubing along a moving region of occlusion to move fluid through the tubing.
One of the difficulties of infusion systems is the evaluation of the condition of the fluid flow upstream of the pump. Where an occlusion of the infusion tube exists upstream of the pump, the pump will not succeed in infusing the parenteral fluid to the patient even though the pump may continue to operate. Similarly, when the parenteral fluid supply becomes depleted, the pump may also continue to operate, however no parenteral fluid will be administered to the patient.
One previous method for detecting a decrease in the fluid supply or an upstream occlusion was visual observation of a drip chamber. However, visually verifying the existence of drops places an undesirable burden on the hospital staff.
In infusion systems utilizing peristaltic pumps, detection of upstream occlusions has been accomplished through the use of an opto-electric drop detector combined with a drip chamber. The opto-electric drop detector detects upstream occlusions, such as occlusions caused by a clamp or kink in the upstream tubing, by detecting an absence of drops. However, the opto-electric drop detector has several disadvantages. Significant movement of the IV administration set can cause a surplus of drops to fall from the drop former or can interrupt the drop formation, thereby causing inaccurate drop counts and false alarms. Ambient light can also interfere with the accuracy of an optical drop sensor.
Another method for detecting upstream occlusions is to incorporate a pressure sensor into the pumping mechanism of the infusion pump. In one such device, a pressure transducer is placed in the middle of the pumping area, allowing direct measurement of the pressure in the pump segment of the fluid tube. The resulting measurement is indicative of the inlet pressure. However, this method can adversely affect flow uniformity and may require substantial modifications to the pumping mechanism.
Pump systems have been disclosed that include a downstream pressure sensor used for detecting improper fluid communication with the patient. Such systems include U.S. Pat. No. 4,743,228 to Butterfield; U.S. Pat. No. 4,460,355 to Layman; U.S. Pat. No. 4,534,756 to Nelson; and U.S. Pat. No. 5,356,378 to Doan.
In operation, peristaltic pump mechanisms sequentially occlude the pumping segment of the tube, also known as the pumping control segment, to alternately expose the pumping segment to fluid communication with the upstream and downstream portions of the infusion tube. The pumping segment is at upstream pressure when exposed to the upstream portion of the fluid line. When the pumping segment is subsequently exposed to the downstream portion, the fluid within the pumping segment, which was at upstream pressure, causes a change in pressure, i.e., a pressure difference, as the pumping segment pressure equalizes with the downstream portion.
There have been pump systems with downstream pressure sensors that have utilized analysis of such pressure differences to detect upstream occlusions. If a large negative pressure difference occurs, an upstream occlusion is presumed. However, pumping into high downstream pressures can create pressure waveform conditions, including drops in pressure, that mimic the appearance of true upstream occlusions. Additionally, pressure sensors may exhibit substantial offset errors that can also mimic upstream occlusion conditions. Pressure sensors used with infusion systems may express variance in their readings that can deviate substantially from the desired values. Such variances, which may be produced by temperature differences or other factors such as the composition of the infusion tube, can cause false alarms. These false alarms detract from the usefulness of an occlusion detection system. While in some cases these variances may be reduced through compensation circuits or closer tolerances on various mechanical and circuit elements, these approaches may substantially complicate the device.
Accordingly, it is desirable to use an upstream pressure sensor having accuracy requirements less stringent than absolute values or threshold values while avoiding false alarms.
Hence, those skilled in the art have recognized the need for a infusion tube monitoring system that can automatically detect upstream infusion tube occlusions while minimizing false alarms. Additionally, those skilled in the art have recognized a need to reduce the cost of a system capable of determining such upstream infusion tube conditions. The present invention fulfills these needs and others.
Other advantages and aspects of the present invention will become apparent upon reading the following description of the drawings and detailed description of the invention.
Accordingly, the present invention provides a method and system for the detection of upstream occlusions in flexible infusion tubing so as to allow for the minimization of false occlusion alarms. The method is used within an occlusion detection system. The occlusion detection system for detecting occlusions inhibiting a fluid flowing in a tube adapted for connection to a fluid pump has a pressure sensor for releasable attachment to the tube upstream of the fluid pump for monitoring a negative pressure condition. The occlusion detection system contains a transducer operably attached to the pressure sensor, the transducer converts the monitored negative pressure condition in a fluid tube into a usable signal. The occlusion detection system further includes an alarm module that is responsive to a signal indicating that the negative pressure condition is outside an acceptable range.
In one aspect of the present invention, the transducer is attached to the pressure sensor that makes contact with the flexible infusion tube. Several types of transducers may be used with the occlusion detection system. These include, but are not limited to, a force sensing resistor, a piezoresistive sensor, a piezoelectric sensor, a diaphragm piston gauge, a bending beam gauge, a strain gauge, a hall-effect sensor, a xc2xc bridge strain gauge, a xc2xd bridge strain gauge, or a full bridge strain gauge. In another aspect of the present invention, the fluid pump may be selected from the group consisting of a peristaltic pump, a roller pump, an expulsor pump, a finger pump and a piston cassette pump. In yet another aspect of the present invention, the pressure sensor can be calibrated with a calibration gauge. In some applications, the signaling of an upstream occlusion may be over a network.
In addition to the above, the method of detecting an occlusion within a flexible infusion tube includes the steps of measuring a first sample indicating a pressure in the tube relative to a first instance in time; measuring a second sample indicating a pressure in the tube relative to a second instance in time; measuring a third sample indicating a pressure in the tube relative to a third instance in time; creating a first difference value of the first sample to the second sample; creating a second difference value of the second sample to the third sample; comparing the first difference value to a percentage of the second difference value; and generating an occlusion signal in response to the step of comparing the first difference value to the second difference value.
In yet another aspect of the present invention, the method of detecting an occlusion within a flexible infusion tube includes the steps of measuring a first sample indicating a pressure in the tube relative to a first instance in time; measuring a second sample indicating a pressure in the tube relative to a second instance in time; creating a first difference value of the first sample to a second sample; comparing the first difference value to a percentage of a second difference value; and generating an occlusion signal in response to the step of comparing the first difference value to a second difference value.
In another aspect of the present invention, the system for detecting an occlusion within a flexible infusion tube includes a measuring device for measuring a first sample indicating a pressure in the tube relative to a first instance in time; the measuring device also measuring a second sample indicating a pressure in the tube relative to a second instance in time; the measuring device also measuring a third sample indicating a pressure in the tube relative to a third instance in time; the measuring device also creating a first difference value of the first sample to the second sample; the measuring device also creating a second difference value of the second sample to the third sample; the measuring device also comparing the first difference value to a percentage of the second difference value; and an alarm module generating an occlusion signal in response to the measuring device also comparing the first difference value to the second difference value.
In yet another aspect of the present invention, the system for detecting an occlusion within a flexible infusion tube includes a measuring device for measuring a first sample indicating a pressure in the tube relative to a first instance in time; the measuring device also measuring a second sample indicating a pressure in the tube relative to a second instance in time; the measuring device also creating a first difference value of the first sample to a second sample; the measuring device also comparing the first difference value to a percentage of a second difference value; and an alarm module generating an occlusion signal in response to the measuring device also comparing the first difference value to the second difference value.